No takers on this question? I investigated further and it seems that
this is a specific problem with iputils-ping. It seems that regardless
of the supplied interface name, the source IP is chosen to be closest t
the default gateway. OTOH my ability to follow C code is next to
minimal, and I would really appreciate if someone can confirm this. Here
is the part I believe is relevant:
if (source.sin_addr.s_addr == 0) {
socklen_t alen;
struct sockaddr_in dst = whereto;
int probe_fd = socket(AF_INET, SOCK_DGRAM, 0);
if (probe_fd < 0) {
perror("socket");
exit(2);
}
if (device) {
struct ifreq ifr;
memset(&ifr, 0, sizeof(ifr));
strncpy(ifr.ifr_name, device, IFNAMSIZ-1);
if (setsockopt(probe_fd, SOL_SOCKET, SO_BINDTODEVICE, device,
strlen(device)+1) == -1) {
if (IN_MULTICAST(ntohl(dst.sin_addr.s_addr))) {
struct ip_mreqn imr;
if (ioctl(probe_fd, SIOCGIFINDEX, &ifr) < 0) {
fprintf(stderr, "ping: unknown iface %s\n", device);
exit(2);
}
memset(&imr, 0, sizeof(imr));
imr.imr_ifindex = ifr.ifr_ifindex;
if (setsockopt(probe_fd, SOL_IP, IP_MULTICAST_IF, &imr, sizeof(imr))
== -1) {
perror("ping: IP_MULTICAST_IF");
exit(2);
}
}
}
}
if (settos &&
setsockopt(probe_fd, IPPROTO_IP, IP_TOS, (char *)&settos, sizeof(int))
< 0)
perror("Warning: error setting QOS sockopts");
dst.sin_port = htons(1025);
if (nroute)
dst.sin_addr.s_addr = route[0];
if (connect(probe_fd, (struct sockaddr*)&dst, sizeof(dst)) == -1) {
if (errno == EACCES) {
if (broadcast_pings == 0) {
fprintf(stderr, "Do you want to ping broadcast? Then -b\n");
exit(2);
}
fprintf(stderr, "WARNING: pinging broadcast address\n");
if (setsockopt(probe_fd, SOL_SOCKET, SO_BROADCAST,
&broadcast_pings, sizeof(broadcast_pings)) < 0) {
perror ("can't set broadcasting");
exit(2);
}
if (connect(probe_fd, (struct sockaddr*)&dst, sizeof(dst)) == -1) {
perror("connect");
exit(2);
}
} else {
perror("connect");
exit(2);
}
}
alen = sizeof(source);
if (getsockname(probe_fd, (struct sockaddr*)&source, &alen) == -1) {
perror("getsockname");
exit(2);
}
source.sin_port = 0;
close(probe_fd);
} while (0);
Peter Rabbitson wrote:
Hi,
I have a testing multihome setup, with the default gateway being one of
the links and using policy routing to honor requests for a specific
link. Everything works as expected when I request a specific IP to bind
to. But if I request a specific interface things fall apart in ways that
I can not explain:
default gw (WORKS)
----------
rabbit@Thesaurus:~$ ping -c 1 yahoo.com
PING yahoo.com (216.109.112.135) 56(84) bytes of data.
64 bytes from w2.rc.vip.dcn.yahoo.com (216.109.112.135): icmp_seq=1
ttl=48 time=142 ms
request IP on same link as default gw (WORKS)
-------------------------------------
rabbit@Thesaurus:~$ ping -I 192.168.9.102 -c 1 yahoo.com
PING yahoo.com (66.94.234.13) from 192.168.9.102 : 56(84) bytes of data.
64 bytes from w2.rc.vip.scd.yahoo.com (66.94.234.13): icmp_seq=1 ttl=47
time=176 ms
request IP on secondary link (WORKS)
----------------------------
rabbit@Thesaurus:~$ ping -I 172.16.0.2 -c 1 yahoo.com
PING yahoo.com (216.109.112.135) from 172.16.0.2 : 56(84) bytes of data.
64 bytes from w2.rc.vip.dcn.yahoo.com (216.109.112.135): icmp_seq=1
ttl=47 time=146 ms
request interface of default gw link (WORKS)
------------------------------------
rabbit@Thesaurus:~$ ping -I eth1 -c 1 yahoo.com
PING yahoo.com (66.94.234.13) from 192.168.9.102 eth1: 56(84) bytes of
data.
64 bytes from w2.rc.vip.scd.yahoo.com (66.94.234.13): icmp_seq=1 ttl=47
time=176 ms
request secondary interface (FAILS)
---------------------------
rabbit@Thesaurus:~$ ping -I eth0 -c 1 yahoo.com
PING yahoo.com (216.109.112.135) from 192.168.9.102 eth0: 56(84) bytes
of data.
From 172.16.0.2 icmp_seq=1 Destination Host Unreachable
I went over the setup again and again, but I can't figure out why the
last ping attempt fails. Any pointers are welcome!
Thanks
Peter
Here is the setup:
ip addr
----------
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:11:09:8d:4f:c1 brd ff:ff:ff:ff:ff:ff
inet 172.16.0.2/24 brd 172.16.0.255 scope global eth0
3: eth1: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:04:e2:80:b4:97 brd ff:ff:ff:ff:ff:ff
inet 192.168.9.102/24 brd 192.168.9.255 scope global eth1
ip ro show table all
-----------------------
default via 172.16.0.1 dev eth0 table 10
default via 192.168.9.1 dev eth1 table 20
default via 192.168.9.1 dev eth1 table default
172.16.0.0/24 dev eth0 proto kernel scope link src 172.16.0.2
192.168.9.0/24 dev eth1 proto kernel scope link src 192.168.9.102
broadcast 127.255.255.255 dev lo table local proto kernel scope link
src 127.0.0.1
broadcast 192.168.9.0 dev eth1 table local proto kernel scope link
src 192.168.9.102
broadcast 172.16.0.0 dev eth0 table local proto kernel scope link src
172.16.0.2
local 192.168.9.102 dev eth1 table local proto kernel scope host src
192.168.9.102
local 172.16.0.2 dev eth0 table local proto kernel scope host src
172.16.0.2
broadcast 192.168.9.255 dev eth1 table local proto kernel scope link
src 192.168.9.102
broadcast 172.16.0.255 dev eth0 table local proto kernel scope link
src 172.16.0.2
broadcast 127.0.0.0 dev lo table local proto kernel scope link src
127.0.0.1
local 127.0.0.1 dev lo table local proto kernel scope host src
127.0.0.1
local 127.0.0.0/8 dev lo table local proto kernel scope host src
127.0.0.1
ip ru
-----
0: from all lookup local
5: from all lookup main
10: from all iif eth0 lookup 10
11: from 172.16.0.0/24 lookup 10
20: from all iif eth1 lookup 20
21: from 192.168.9.0/24 lookup 20
100: from all lookup default
no netfilter rules of any sort (all policies set at ACCEPT)
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